In the context of the optimisation of fuel assembly performance of Pressurised Water Reactor, the “laboratoire d’Essais Thermo-hydraulique et Hydromécanique (LETH)” is in charge to develop a new research program based on a new test section named SEQUIN.
SEQUIN is a CFD grade experiments designed to study the turbulent flow at the entrance of fuel assemblies. It is representative of geometric and hydraulic parameters of the industrial object with a dilated scale of 2.81. Moreover, to permit optical measurements of the flow (e.g. LDV, PIV, Holography) SEQUIN is a fully transparent test section.
The objective of this PhD thesis is the exploration, quantification and analyse of the turbulent flow within SEQUIN. This is a complex geometry with a succession of different types of flows and/or obstacles, e.g. jets, quarter of foot, perforated plate, entrance of rod bundle, grids. The study of the structure of velocity fields (and possibly acceleration fields and pressure fluid), pressure fluctuations at the wall, pressure drops, forces applied on the ¼ foot will be performed over more than one decade of turbulent Reynolds numbers. For example, it will permit to explore the role of pressure fluctuations at the entrance of fuel assemblies on rods vibrations and their origin. To our knowledge, this new experiment will be the first analytical experiment of its kind. It will permit in-depth exploration of the turbulent flow phenomena with advanced measurements of the physical parameter of interest (velocity, pressure, forces). Such level of details will contribute to the understanding of the turbulent flow at the entrance of fuel assemblies and its consequences for unsteady forces applied.
In addition to the exploration of the flow physic, the CFD grade level of SEQUIN experiment and the possibility to work at different Reynolds number will permit to improve the numerical modelling (industrial collaborations) of this kind of flows. Indeed, due to their geometrical complexity (details and size), they are still not accessible to Direct Numerical Simulations (DNS) at large Reynolds numbers. The building of an experimental database for the validation of CFD codes in complex geometries will complement the physical description of the flow.
The student will contribute to the setting up of the instrumentation and the definition of experimental campaigns. He/she will process the data with numerical codes that he/she will have developed. He/she will analyse his/her results in details, confront them to the stat of the art of fuel assemblies and to generic flows associated the different geometries of SEQUIN before submitting them for publication in international journals.
• N. Turankok, F. Moreno, S. Bantiche, F. Bazin, V. Biscay, T. Lohez, D. Picard, S. Testaniere, L. Rossi, 2020. “Unsteady pressure and velocity measurements in 5x5 rods bundle using grids with and without mixing vanes”. Nuclear Engineering and Design, 364(110687).
• N. Turankok, T. Lohez, F. Bazin, V. Biscay, L. Rossi, 2021. “Exploration of Frequencies Peaks Observed On Local Wall Pressure Measurements by Time Resolved Velocity Fields Measurements in Complex Flows”. Experiments in Fluids, 62.